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Dynamic property attribute evaluation at run and desing timeBy mileniEver wanted to hide, propertect properties at design or runtime using other property value? Here is the answer!!! |
C# 2.0, C#, Windows, .NET, .NET 1.1, .NET 2.0VS.NET2003, Visual Studio, Dev Posted: 21 Mar 2007 Updated: 21 Mar 2007 Views: 15,003 Bookmarked: 21 times |
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When Formatable is False, only Text is visible
But when Formatable is True, Text is protected and Format shows up ;)
Introduction
In my work very often I have to resolve this kind of problems so after some reading, copying, googling, etc... Wow idea comes up!
Background
ImplementingICustomTypeDescriptor interface on any class we can provide properties to PropertyGrid control in dynamic way. So lets code that interface.public class SomeClass : ICustomTypeDescriptor
{
public EventDescriptorCollection GetEvents(Attribute[] attributes)
{
return TypeDescriptor.GetEvents(this, attributes, true);
}
/* ... so we arrive at ... */
public PropertyDescriptorCollection GetProperties()
{
// use new implemented class to get properties
return DynamicTypeDescriptor.GetProperties(this);
}
}
So, what is DynamicTypeDescriptor class here for? This class substitutes standard TypeDescriptor.GetProperties(...) behaviour.public static PropertyDescriptorCollection GetProperties(object component)
{
// hold all properties found
PropertyInfo[] propsInfo = component.GetType().GetProperties(BindingFlags.Public|BindingFlags.Instance);
ArrayList list = new ArrayList(propsInfo.Length);
// loop properties
foreach(PropertyInfo prop in propsInfo)
{
// get all property attributes and check for "dynamics"
ArrayList attributeList = new ArrayList();
foreach(Attribute attrib in prop.GetCustomAttributes(true))
{
// if is dynamic one then evaluate it
if (attrib is DependsOnPropertyAttribute)
attributeList.Add(((DependsOnPropertyAttribute)attrib).Evaluate(component));
else
attributeList.Add(attrib);
}
list.Add(new PropertyInfoDescriptor(prop, (Attribute[])attributeList.ToArray(typeof(Attribute))));
}
return new PropertyDescriptorCollection((PropertyDescriptor[])list.ToArray(typeof(PropertyDescriptor)));
}
You may said, but what DependsOnPropertyAttribute stands for?
/// <summary> /// Base class for all dynamic attributes. /// Only properties can use this attribute. /// </summary> [AttributeUsage(AttributeTargets.Property)] public abstract class DependsOnPropertyAttribute : Attribute { /// <summary> /// Create new instance of class /// </summary> /// <param name="expression">Property name</param> protected DependsOnPropertyAttribute(string property) : base() { _property = property; _index = null; } /// <summary> /// Create new instance of class /// </summary> /// <param name="property">Property name</param> /// <param name="index">Property element index</param> protected DependsOnPropertyAttribute(string property, int index) { _property = property; _index = new object[] {index}; } private string _property; private object[] _index; /// <summary> /// Evaluate attribute using property container supplied /// </summary> /// <param name="container">Object that contains property to evaluate</param> /// <returns>Dynamically evaluated attribute</returns> public Attribute Evaluate(object container) { return OnEvaluateComplete(RuntimeEvaluator.Eval(container, _property, _index)); } /// <summary> /// Specific dynamic attribute check implementation /// </summary> /// <param name="value">Evaluated value</param> /// <returns>Dynamically evaluated attribute</returns> protected abstract Attribute OnEvaluateComplete(object value); private class RuntimeEvaluator { public static object Eval(object container, string property, object[] index) { PropertyInfo pInfo = container.GetType().GetProperty(property); if (pInfo != null) return pInfo.GetValue(container, index); return null; } } }
This class defines abstract implemenentation for all DynamicAttributes. In my example there are two implemented attributes: DynamicBrowsableAttribute and DynamicReadOnlyAttribute.
Sample implementation for abstract OnEvaluateComplete method:
protected override Attribute OnEvaluateComplete(object value) { Attribute output; try { // check if value is provided if (value == null) value = false; // asume default // create attribute output = new ReadOnlyAttribute((bool)value); } catch { output = new ReadOnlyAttribute(false); } return output; }
Using the code
To use code you will have to create some class with public properties. On property that others depends on, insert RefreshProperties(RefreshProperties.All) attribute so property grid will be auto refreshed and will requery your properties. To provide dynamic functionality implement ICustomTypeDescriptor interface in your class. Now on you dynamically provide properties to property grid, easy yeah!
Insert DynamicAttribute on dynamic properties like this DynamicBrowsable("property name"), where property name is substituted with name of property that this one depends on. In my case property Format have DynamicBrowsable("Formatable") attribute set.
Points of Interest
You can see how to implement ICustomTypeDescriptor interface, how to provide new Attributes and how to play with PropertyGrid control.
History
21/03/2007 - First release.
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. But maybe somebody will find usefull my work.
. 
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Last Updated: 21 Mar 2007 Editor: |
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